let _Vue = null
export default class VueRouter {
    static install(Vue) {

        // //1 判断当前插件是否被安装
        if (VueRouter.install.installed) {
            return;
        }
        VueRouter.install.installed = true
        //2 把Vue的构造函数记录在全局
        _Vue = Vue

        //3 把创建Vue的实例传入的router对象注入到Vue实例
        // _Vue.prototype.$router = this.$options.router  ( this应该是vue实例，而不是vueRouter构造函数 )
        _Vue.mixin({
            beforeCreate() {
                if (this.$options.router) {
                    _Vue.prototype.$router = this.$options.router
                    this.$options.router.init()
                }

            }
        })
    }
    constructor(options) {
        this.options = options
        this.routeMap = {}
        // observable
        this.data = _Vue.observable({
            current: "/"
        })

    }
    init() {
        this.createRouteMap()
        this.initComponent(_Vue)
        this.initEvent()
    }
    createRouteMap() {
        //遍历所有的路由规则 吧路由规则解析成键值对的形式存储到routeMap中
        this.options.routes.forEach(route => {
            this.routeMap[route.path] = route.component
        });
    }
    initComponent(Vue) {
        Vue.component("router-link", {
            props: {
                to: String
            },
            // template: '<a :href="to"><slot></slot></a>'
            render(h) {
                return h('a', {
                    attrs: {
                        href: this.$router.options.mode == 'history' ? this.to : '#' + this.to
                    },
                    on: {
                        click: this.clickHandler
                    }
                }, [this.$slots.default])
            },
            methods: {
                clickHandler(e) {
                    if (this.$router.options.mode == 'history') {
                        history.pushState({}, '', this.to)
                        this.$router.data.current = this.to
                        e.preventDefault()
                    } else {
                        this.$router.data.current = this.to
                    }
                }
            }
        })
        const self = this

        Vue.component("router-view", {
            render(h) {
                // self.data.current
                const cm = self.routeMap[self.data.current]
                return h(cm)
            }
        })
    }
    initEvent() {
        //点击前进
        window.addEventListener('popstate', () => {
            this.data.current = window.location.pathname

        })
    }


}